Parameter Uncertainty And Nonstationarity In Regional Rainfall Frequency In Qu River Basin, East China

Traditionally, regional frequency analysis was developed for stable environmental conditions. Nevertheless, recent studies have identified significant changes in hydrological records under changing environments. Besides, uncertainty in hydrological frequency analysis is persistent. This study aims to investigate the impact of one of the most important uncertainty sources, parameter uncertainty, together with nonstationarity, on design rainfall depth in Qu River Basin, East China. A spatial bootstrap is first proposed to analyze the uncertainty of design rainfall depth estimated by at-site frequency analysis and by regional frequency analysis based on L-moments and the index variable method. Meanwhile, a method combining the generalized additive model with a 30-year moving window is employed to analyze nonstationarity existing in an extreme rainfall regime. The results show that the uncertainty of 100-year design rainfall depth due to parameter uncertainty reaches 15.42 and 12.45% with generalized extreme value (GEV) and Pearson type III (PE3) distributions, respectively, on the regional scale, while such uncertainty is up to 19.16% with GEV and 16.17% with PE3 on the at-site scale. Under the nonstationarity condition, the uncertainty of the design rainfall depth with 0.01 annual exceedance probability is 24.83% with GEV and 16.94% with PE3. The uncertainty of the design rainfall depth resulting from parameter uncertainty is less than that from nonstationarity frequency analysis with both GEV and PE3. (C) 2016 American Society of Civil Engineers.